GEOTECHNICAL PROPERTIES OF SALT MARSH AND TIDAL FLAT SUBSTRATES AT TILLINGHAM, ESSEX, UK.

The influence of grain size and frictional/cohesional shear strength components on UK salt marsh substrate stability

10.5194/egusphere-egu2020-17681 ◽

2020 ◽

Author(s):

Helen Brooks ◽

Iris Moeller ◽

Tom Spencer ◽

Kate Royse

Keyword(s):

Shear Strength ◽

Salt Marsh ◽

Internal Friction ◽

Water Levels ◽

Systematic Research ◽

Surface Erosion ◽

Marsh Edge ◽

Angle Of Internal Friction ◽

Erosion Processes ◽

Ring Shear

Salt marshes attenuate waves and currents, thus protecting landward-lying constructed defences and the hinterland from incoming waves and extreme water levels. As such, understanding the stability of the marsh sedimentary platform is important, particularly as marsh edge erosion is common on many shores. To understand why marshes are losing material from their exposed fringes, we must better understand the relations between the marsh fabric and incoming hydrodynamic energy; this is likely to be strongly influenced by marsh biological, geochemical and sedimentological/geotechnical properties. Currently there is little systematic research into the within- and between-marsh variability in these properties and how they affect both marsh edge and marsh surface erosion processes.&#160;We compare Tillingham marsh, eastern England, where the sediment is clay/silt-dominated and the marsh canopy is species-rich, to Warton marsh, Morecambe Bay, NW England, where the sediment is sand/silt-dominated and the vegetation species-poor. We determine soil shear strength by applying geotechnical methods which, to the best of our knowledge, have not previously been applied to salt marsh environments. Shear box and ring shear tests are used to determine the natural- and residual (i.e. post-failure) shear strength of the substrate, respectively. This is expressed as the cohesion of the sediment and the angle of internal friction. We demonstrate that the ring shear test consistently returns a lower angle of internal friction for the substrate, which is expected for the residual angle of internal friction. However, we are also able to link this reduction in the angle of internal friction to substrate composition (e.g. root content, organic matter and particle size distribution). This enhanced methodological understanding will improve our comprehension of marsh resistance to edge erosion and thus our ability to predict future erosion. Ultimately, accurate measurements of the shear strength of natural foreshores are essential for the informed implementation of nature-based coastal flood defences, including &#8216;de-embankment&#8217;/&#8216;managed realignment&#8217; schemes.

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Topological and Morphological Controls on Morphodynamics of Salt Marsh Interiors

Journal of Marine Science and Engineering ◽

10.3390/jmse9030311 ◽

2021 ◽

Vol 9 (3) ◽

pp. 311

Author(s):

Ben R. Evans ◽

Iris Möller ◽

Tom Spencer

Keyword(s):

Salt Marsh ◽

Salt Marshes ◽

East Coast ◽

Marsh Surface ◽

Coastal Environments ◽

Coastal System ◽

Morphological Segmentation ◽

The Usa ◽

The Uk ◽

Over Time

Salt marshes are important coastal environments and provide multiple benefits to society. They are considered to be declining in extent globally, including on the UK east coast. The dynamics and characteristics of interior parts of salt marsh systems are spatially variable and can fundamentally affect biotic distributions and the way in which the landscape delivers ecosystem services. It is therefore important to understand, and be able to predict, how these landscape configurations may evolve over time and where the greatest dynamism will occur. This study estimates morphodynamic changes in salt marsh areas for a regional domain over a multi-decadal timescale. We demonstrate at a landscape scale that relationships exist between the topology and morphology of a salt marsh and changes in its condition over time. We present an inherently scalable satellite-derived measure of change in marsh platform integrity that allows the monitoring of changes in marsh condition. We then demonstrate that easily derived geospatial and morphometric parameters can be used to determine the probability of marsh degradation. We draw comparisons with previous work conducted on the east coast of the USA, finding differences in marsh responses according to their position within the wider coastal system between the two regions, but relatively consistent in relation to the within-marsh situation. We describe the sub-pixel-scale marsh morphometry using a morphological segmentation algorithm applied to 25 cm-resolution maps of vegetated marsh surface. We also find strong relationships between morphometric indices and change in marsh platform integrity which allow for the inference of past dynamism but also suggest that current morphology may be predictive of future change. We thus provide insight into the factors governing marsh degradation that will assist the anticipation of adverse changes to the attributes and functions of these critical coastal environments and inform ongoing ecogeomorphic modelling developments.

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Hitchhiking Halophytes in Wrack and Sediment-Laden Ice Blocks Contribute To Tidal Marsh Development in The Upper Bay of Fundy.

10.21203/rs.3.rs-1021544/v1 ◽

2021 ◽

Author(s):

Jeremy Lundholm ◽

Tasha R.M. Rabinowitz ◽

Lyndsay Greene ◽

Alisha D. Glogowski ◽

Tony Bowron ◽

...

Keyword(s):

Salt Marsh ◽

Salt Marshes ◽

Coastal Wetland ◽

Marsh Surface ◽

Plant Colonization ◽

Bay Of Fundy ◽

Plant Debris ◽

Salt Marsh Restoration ◽

Potential Source ◽

Total Sediment

Abstract Salt marshes are a type of coastal wetland that are affected by dynamic coastal processes. Ice blocks and wrack (mats of plant debris) regularly float onto northern marshes and become stranded, affecting vegetation and soil accretion. There is little research regarding the capacity of ice and wrack to transport viable plant propagules onto marshes where they can colonize, which may be particularly important at barren new salt marsh restoration sites. Contributions of sediment by ice may also be important at restoration sites to raise the marsh platform to elevations appropriate for plant colonization. We collected ice (n = 27) and wrack (n = 18) samples at marshes in the Bay of Fundy, ran germination trials with the contents, and measured the quantity of sediment in the ice. We found viable propagules from halophytic and non-halophytic species in wrack, and viable propagules of Sporobolus pumilus in ice. Additionally, we found sediment densities between 0.01 and 4.75 g·cm−3 in ice blocks that translated to 26.61 – 21,483.59 kg of total sediment per block, representing a large source of sediment. We found that the number of germinating propagules could not be predicted by wrack size, and that pH, sediment density, sediment weight in ice blocks were variable across the marsh surface, while ice salinity was negatively correlated with elevation and distance from creek. Our results indicate that ice and wrack represent a potential source for vegetation colonization at salt marsh sites and highlights their contributions to facilitating vegetation colonization through building marsh soils.

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How do storm events and fair-weather conditions affect sedimentation patterns on salt marshes?

10.5194/egusphere-egu2020-10828 ◽

2020 ◽

Author(s):

Davide Tognin ◽

Mattia Pivato ◽

Andrea D'Alpaos ◽

Luca Carniello

Keyword(s):

Salt Marsh ◽

Salt Marshes ◽

Weather Conditions ◽

Marsh Surface ◽

Sediment Traps ◽

Vertical Accretion ◽

Storm Events ◽

Fair Weather ◽

Short Term ◽

Intense Storm

Coastal salt marshes are extremely important ecosystems, occupying the transitional zone between submerged and emerged environments. Since salt marshes are based on a delicate balance between hydrodynamics and sedimentary processes, their future is heavily affected by relative sea-level rise (RSLR), caused by both subsidence and eustatism. If vertical accretion is sufficient, salt marshes can keep pace with RSLR; otherwise, lack of sediment input can eventually lead to plant death and marsh drowning, transforming these landforms into tidal flats and subtidal platforms. Resuspension driven by intense meteorological events can represent an important source of sediment for salt marsh accretion in tidal environments characterized by negligible fluvial sediment supply. However, it is not yet clear what is the mutual role and relative contribution of intense storm events and fair-weather conditions in terms of sedimentation patterns. To better understand sedimentation dynamics on salt marshes, we stared a field campaign in October 2018 to measure vertical accretion rate and sediment accumulation.In the Venice lagoon (Italy), which is the largest lagoon in the Mediterranean sea and is characterized by a semi-diurnal, microtidal regime, we selected three study areas: the San Felice and Sant&#8217;Erasmo salt marshes in the northern lagoon and the Conche salt marsh in the southern lagoon. Subsidence at all these study sites ranges between 1.0 and 2.0 mm yr-1, and the rate of sea-level rise is of about 2.0 mm yr-1, for a total rate of RSLR of about 3.0-4.0 mm yr-1. At each study area, we considered different transects, where we installed three measurement stations located respectively at 2.5 m, 7.5 m, and 27.5 m from the salt marsh margin. We equipped each station with an artificial marker horizon laid down on the marsh surface to measure the vertical accretion, and three sediment traps for measuring the short-term sedimentation. The material deposited in two sediment traps is collected monthly or after any single storm, whereas sediment deposited in the third trap is collected once a year, in order to compare sediment deposition dynamics at short (single storm event) and annual time scales. We measure accretion rate, grain size distribution, organic and inorganic content.Short-term sedimentation displays a very high variability (0 &#8211; 320 g d-1 m-2) highlighting the importance of particularly intense storm events in resuspending and transporting sediment from tidal flats to the salt-marsh surface. In particular, during the storm events occurred in October 2018 and November 2019, sedimentation increases significantly and displays values much higher compared to fair-weather periods. According to our analysis, sedimentation grows exponentially with daily mean inundation time. Even if the inner part of the salt marsh is characterized by lower elevation and, hence, by greater inundation time, sedimentation shows smaller values compared to the salt marsh margin, since suspended material settles close to the margin and decreases towards the inner part of the marsh.

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Unsupervised detection of salt marsh platforms: a topographic method

10.5194/esurf-2017-60 ◽

2017 ◽

Author(s):

Guillaume C. H. Goodwin ◽

Simon M. Mudd ◽

Fiona J. Clubb

Keyword(s):

Salt Marsh ◽

Salt Marshes ◽

Tidal Flat ◽

Near Infrared ◽

Numerical Models ◽

Storm Surges ◽

Unsupervised Classification ◽

Marsh Vegetation ◽

Local Maxima ◽

Topographic Evolution

Abstract. Salt marshes filter pollutants, protect coastlines against storm surges, and sequester carbon, yet are under threat from sea level rise and anthropogenic modification. The productivity and even survival of salt marsh vegetation depends on the topographic evolution of marsh platforms. Quantifying marsh platform topography is vital for improving the management of these valuable landscapes. Determining platform boundaries currently relies on supervised classification methods requiring near-infrared data to detect vegetation, or demands labor-intensive field surveys and digitization. We propose a novel, unsupervised method to reproducibly isolate saltmarsh scarps and platforms from a DEM, referred to as Topographic Identification of Platforms (TIP). Field observations and numerical models show that saltmarshes mature into sub-horizontal platforms delineated by sub-vertical scarps: based on this premise, we identify scarps as lines of local maxima on a slope raster, then fill landmasses from the scarps upward, thus isolating mature marsh platforms. We test the TIP method using lidar-derived DEMs from six saltmarshes in England with varying tidal ranges and geometries, for which topographic platforms were manually distinguished from tidal flats. Agreement between manual and unsupervised classification exceeds 94 % for DEM resolutions of 1 m, with all but one sites maintaining an accuracy superior to 90 % for resolutions up to 3 m. For resolutions of 1 m, platforms detected with the TIP method are comparable in surface area to digitized platforms, and have similar elevation distributions. We also find that our method allows the accurate detection of local bloc failures as small as 3 times the DEM resolution. Detailed inspection reveals that although tidal creeks were digitized as part of the marsh platform, unsupervised classification categorizes them as part of the tidal flat, causing an increase in false negatives and overall platform perimeter. This suggests our method would have increased accuracy if used in combination with existing creek detection algorithms. Fallen blocs and high tidal flat portions, associated with potential pioneer zones, may also be areas of discordance between our method and supervised mapping. Although pioneer zones prove difficult to classify using a topographic method, it also suggests that these transition areas should be considered when analysing erosion and accretion processes, particularly in the case of incipient marsh platforms. Ultimately, we have shown that unsupervised classification of marsh platforms from high-resolution topography is possible and sufficient to monitor and analyze topographic evolution.

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Unsupervised detection of salt marsh platforms: a topographic method

Earth Surface Dynamics ◽

10.5194/esurf-6-239-2018 ◽

2018 ◽

Vol 6 (1) ◽

pp. 239-255 ◽

Cited By ~ 5

Author(s):

Guillaume C. H. Goodwin ◽

Simon M. Mudd ◽

Fiona J. Clubb

Keyword(s):

Salt Marsh ◽

Salt Marshes ◽

Tidal Flat ◽

Near Infrared ◽

Numerical Models ◽

Storm Surges ◽

Unsupervised Classification ◽

Local Maxima ◽

Elevation Model ◽

Topographic Evolution

Abstract. Salt marshes filter pollutants, protect coastlines against storm surges, and sequester carbon, yet are under threat from sea level rise and anthropogenic modification. The sustained existence of the salt marsh ecosystem depends on the topographic evolution of marsh platforms. Quantifying marsh platform topography is vital for improving the management of these valuable landscapes. The determination of platform boundaries currently relies on supervised classification methods requiring near-infrared data to detect vegetation, or demands labour-intensive field surveys and digitisation. We propose a novel, unsupervised method to reproducibly isolate salt marsh scarps and platforms from a digital elevation model (DEM), referred to as Topographic Identification of Platforms (TIP). Field observations and numerical models show that salt marshes mature into subhorizontal platforms delineated by subvertical scarps. Based on this premise, we identify scarps as lines of local maxima on a slope raster, then fill landmasses from the scarps upward, thus isolating mature marsh platforms. We test the TIP method using lidar-derived DEMs from six salt marshes in England with varying tidal ranges and geometries, for which topographic platforms were manually isolated from tidal flats. Agreement between manual and unsupervised classification exceeds 94 % for DEM resolutions of 1 m, with all but one site maintaining an accuracy superior to 90 % for resolutions up to 3 m. For resolutions of 1 m, platforms detected with the TIP method are comparable in surface area to digitised platforms and have similar elevation distributions. We also find that our method allows for the accurate detection of local block failures as small as 3 times the DEM resolution. Detailed inspection reveals that although tidal creeks were digitised as part of the marsh platform, unsupervised classification categorises them as part of the tidal flat, causing an increase in false negatives and overall platform perimeter. This suggests our method may benefit from combination with existing creek detection algorithms. Fallen blocks and high tidal flat portions, associated with potential pioneer zones, can also lead to differences between our method and supervised mapping. Although pioneer zones prove difficult to classify using a topographic method, we suggest that these transition areas should be considered when analysing erosion and accretion processes, particularly in the case of incipient marsh platforms. Ultimately, we have shown that unsupervised classification of marsh platforms from high-resolution topography is possible and sufficient to monitor and analyse topographic evolution.

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Identifying Salt Marsh Shorelines from Remotely Sensed Elevation Data and Imagery

Remote Sensing ◽

10.3390/rs11151795 ◽

2019 ◽

Vol 11 (15) ◽

pp. 1795 ◽

Cited By ~ 5

Author(s):

Amy S. Farris ◽

Zafer Defne ◽

Neil K. Ganju

Keyword(s):

Salt Marsh ◽

High Resolution ◽

Salt Marshes ◽

Spatial Scales ◽

Remotely Sensed ◽

Horizontal Resolution ◽

Unmanned Aircraft ◽

Maximum Slope ◽

Marsh Edge ◽

Elevation Data

Salt marshes are valuable ecosystems that are vulnerable to lateral erosion, submergence, and internal disintegration due to sea level rise, storms, and sediment deficits. Because many salt marshes are losing area in response to these factors, it is important to monitor their lateral extent at high resolution over multiple timescales. In this study we describe two methods to calculate the location of the salt marsh shoreline. The marsh edge from elevation data (MEED) method uses remotely sensed elevation data to calculate an objective proxy for the shoreline of a salt marsh. This proxy is the abrupt change in elevation that usually characterizes the seaward edge of a salt marsh, designated the “marsh scarp.” It is detected as the maximum slope along a cross-shore transect between mean high water and mean tide level. The method was tested using lidar topobathymetric and photogrammetric elevation data from Massachusetts, USA. The other method to calculate the salt marsh shoreline is the marsh edge by image processing (MEIP) method which finds the unvegetated/vegetated line. This method applies image classification techniques to multispectral imagery and elevation datasets for edge detection. The method was tested using aerial imagery and coastal elevation data from the Plum Island Estuary in Massachusetts, USA. Both methods calculate a line that closely follows the edge of vegetation seen in imagery. The two methods were compared to each other using high resolution unmanned aircraft systems (UAS) data, and to a heads-up digitized shoreline. The root-mean-square deviation was 0.6 meters between the two methods, and less than 0.43 meters from the digitized shoreline. The MEIP method was also applied to a lower resolution dataset to investigate the effect of horizontal resolution on the results. Both methods provide an accurate, efficient, and objective way to track salt marsh shorelines with spatially intensive data over large spatial scales, which is necessary to evaluate geomorphic change and wetland vulnerability.

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Estimating and Applying Fish and Invertebrate Density and Production Enhancement from Seagrass, Salt Marsh Edge, and Oyster Reef Nursery Habitats in the Gulf of Mexico

Estuaries and Coasts ◽

10.1007/s12237-021-00935-0 ◽

2021 ◽

Author(s):

Philine S. E. zu Ermgassen ◽

Bryan DeAngelis ◽

Jonathan R. Gair ◽

Sophus zu Ermgassen ◽

Ronald Baker ◽

...

Keyword(s):

Salt Marsh ◽

Gulf Of Mexico ◽

Salt Marshes ◽

Fish Habitat ◽

Juvenile Fish ◽

Oyster Reefs ◽

Coastal Habitats ◽

Marsh Edge ◽

Northern Gulf Of Mexico ◽

Nursery Habitats

AbstractSeagrasses, oyster reefs, and salt marshes are critical coastal habitats that support high densities of juvenile fish and invertebrates. Yet which species are enhanced through these nursery habitats, and to what degree, remains largely unquantified. Densities of young-of-year fish and invertebrates in seagrasses, oyster reefs, and salt marsh edges as well as in paired adjacent unstructured habitats of the northern Gulf of Mexico were compiled. Species consistently found at higher densities in the structured habitats were identified, and species-specific growth and mortality models were applied to derive production enhancement estimates arising from this enhanced density. Enhancement levels for fish and invertebrate production were similar for seagrass (1370 [SD 317] g m–2 y–1for 25 enhanced species) and salt marsh edge habitats (1222 [SD 190] g m–2 y–1, 25 spp.), whereas oyster reefs produced ~650 [SD 114] g m–2 y–1(20 spp). This difference was partly due to lower densities of juvenile blue crab (Callinectes sapidus) on oyster reefs, although only oyster reefs enhanced commercially valuable stone crabs (Menippe spp.). The production estimates were applied to Galveston Bay, Texas, and Pensacola Bay, Florida, for species known to recruit consistently in those embayments. These case studies illustrated variability in production enhancement by coastal habitats within the northern Gulf of Mexico. Quantitative estimates of production enhancement within specific embayments can be used to quantify the role of essential fish habitat, inform management decisions, and communicate the value of habitat protection and restoration.

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Erodibility of vertically exposed salt marsh sediments

10.5194/egusphere-egu2020-510 ◽

2020 ◽

Author(s):

Olivia Shears ◽

Iris Möller ◽

Tom Spencer ◽

Katherine Royse ◽

Ben Evans

Keyword(s):

Salt Marsh ◽

Structure From Motion ◽

Salt Marshes ◽

Tidal Flat ◽

Three Dimensional ◽

The United States ◽

Small Scale ◽

External Forcing ◽

Marsh Sediments

Salt marshes are valuable habitats, providing natural coastal protection. However, change in the extent of salt marsh habitats is occurring globally; regional hotspots include widespread losses in Northwest Europe. These lateral losses are occurring despite relative stability in the vertical dimension (i.e. surface elevation and its relation to rising sea levels). Whilst there are an increasing number of studies reporting and quantifying salt marsh losses, the understanding of what controls lateral marsh dynamics remains weak.Numerical models and large-scale experimentation (e.g. in wave flumes) have, to a degree, improved understanding of the mechanisms by which salt marshes can change in the lateral dimension. However, empirical field evidence exploring the role of specific marsh properties and exposure characteristics is lacking. What biophysical factors (i.e. vegetation and sediment characteristics) control internal marsh substrate stability, and how do these factors influence the vulnerability of lateral marsh margins to external forcing?The three-dimensional biophysical response of salt marsh substrates to external forcing representative of tidal flat conditions has been investigated. Intertidal sediment sections were extracted from two contrasting UK salt marsh sites: clay-silt rich Tillingham Marsh, Essex, Southeast England, and sand-dominated Warton Marsh, Morecambe Bay, Northwest England. Vertical sections of sediment were exposed to in-situ external forcing conditions on the fronting tidal flat at Tillingham Marsh. Structure-from-motion digital photogrammetry was used to quantify volumetric and structural changes on the vertical faces of the exposed sedimentary cores at approximately 14-day intervals. Three-dimensional structure-from-motion models were analysed alongside empirical water level measurements and meteorological data. Greater loss of material, typically around root structures, characterised the upper section of the sediment core from Warton Marsh. The Tillingham Marsh sediments were more resistant to erosion, including within the upper section. This indicates possible variability in the mechanical role of rooting structures (as also found in previous work (e.g. Feagin et al. 2009; Ford et al. 2016)), under a different marsh sedimentology.Small-scale marsh stability is thus strongly influenced by physical sedimentology, biological root structures, hydrodynamic sequencing, and the interactions between these factors. A combination of inundation history, bulk sediment strength and belowground vegetation structure is likely to influence salt marsh lateral stability, at least at the cm to m scale. Understanding under which conditions (e.g. location, wave regime) these factors become more or less important, and how these small scale controls scale up to larger scales is crucial towards modelling and predicting future salt marsh change.References:<ul><li>Feagin, R. A., Lozada-Bernard, S. M., Ravens, T. M., M&#246;ller, I., Yeager, K. M., & Baird, A. H. (2009). Does vegetation prevent wave erosion of salt marsh edges? Proceedings of the National Academy of Sciences of the United States of America, 106(25), 10109&#8211;10113. https://doi.org/10.1073/pnas.0901297106</li> <li>Ford, H., Garbutt, A., Ladd, C., Malarkey, J., & Skov, M. W. (2016). Soil stabilization linked to plant diversity and environmental context in coastal wetlands. Journal of Vegetation Science, 27(2), 259&#8211;268. https://doi.org/10.1111/jvs.12367</li> </ul>

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Variability in the erosion response of vertical sections of salt marsh sediments exposed to tidal flat conditions

10.5194/egusphere-egu21-4925 ◽

2021 ◽

Author(s):

Olivia Shears ◽

Iris Möller ◽

Tom Spencer ◽

Ben Evans ◽

Kate Royse

Keyword(s):

Salt Marsh ◽

Salt Marshes ◽

Tidal Flat ◽

Organic Matter Content ◽

Matter Content ◽

Coastal Protection ◽

Sediment Type ◽

Sediment Removal ◽

Substrate Properties ◽

Vertical Sections

Salt marsh ecosystems are important for supporting biodiversity, sequestering carbon and providing natural coastal protection. Evidence for their existing and potential future loss through marginal erosion is therefore of concern. However, the factors governing spatial variability in the rates of erosion at salt marsh margins &#8211; including between creek banks within individual salt marsh sites &#8211; remain relatively poorly understood. Accurate prediction of changes to the marsh edge, and thus marsh areal extent, requires more complete understanding of the dynamics and mechanisms occurring at exposed marsh fronts.In this study, we present observations of the responses of vertical sections of marsh substrate exposed to tidal flat conditions, during a field experiment over a six-month period. Vertical sections were extracted from natural and restored sites at two salt marshes in the UK: Northey Island, eastern England, where sediment is fine-grained, and Hesketh Out Marsh West, north-west England, where sediment is typically sand/silt-dominated. The study specifically investigates the role of different sedimentology and downcore substrate properties, including lamination and rooting structures, on observed change in the exposed vertical sections. Images captured in the field are analysed using structure-from-motion photogrammetry and used to create 3-D models of surface change. This is coupled with laboratory testing of downcore sedimentary characteristics, such as particle size distribution and organic matter content.The study finds that within-core and between-core variability in substrate response to erosive forcing appears to be partly related to variability in sedimentology. Sediment from sand-dominated layers, such as those found in the cores extracted from Hesketh Out Marsh West, was more rapidly and consistently (i.e. across the sediment cores) removed than clay-silt rich sediment. This grain-scale sediment removal resulted in specific morphological responses, whereby &#8216;chunks&#8217; of substrate were lost, creating cavity areas further exposed to hydrodynamic forcing. Intrinsic biophysical characteristics, including sediment type and the presence of vegetation structures, can impact vertical connectivity within salt marsh substrates. Observations of structural change in the vertical sections over the six-month study period suggest that reduced downcore connectivity in restored salt marsh substrates results in increased desiccation, cracking and bulk sediment removal. An improved understanding of how such intrinsic substrate properties impact marsh front dynamics will facilitate more accurate predictions of marsh evolution and potential ecosystem service provision under future conditions.

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